DESCRIPTION: How external growth signals are transmitted from the cell surface to the nucleus is one of the fundamental issues of cell biology. Research in the field of signal transduction has been motivated by the assumption that understanding of the signal pathways responsible for cell growth will yield insight into the uncontrolled growth seen in cancer. Recently, this assumption has been extensively confirmed by the discovery of the detailed molecular mechanism of cell cycle in which a key role is assigned to the protein kinase and its activators and inhibitors. The long-term goal is the rational design of inhibitors for protein kinases. This will incorporate co-crystallization of cAPK with metavanadate and nucleotide "caged" and peptide "caged" complexes, and co-crystallization of a staurosporin class of inhibitors, a derivative of which became a potent specific inhibitor of protein kinase C and EGFR kinase. Co-crystallization with the caged analogs, carried out in collaboration with Professor Roger Goody, is aimed at dynamic analysis of conformational changes of the catalytic core, namely the glycine-rich loop. Co-crystallization of staurosporin inhibitors, carried out in collaboration with Ciba-Geigy A.G., Basil, aims at enhancing the specificity of those inhibitors using crystallography and modeling. The current studies aim at the structural basis of phosphotransfer and substrate recognition of cAPK, the first protein kinase whose structure became known. The three specific aims are: (1) The analysis of conformational changes which the conserved catalytic core undergoes. (2) The structure of the transition state analog. (3) The mechanism of inhibition of catalysis through binding of a potent inhibitor - staurosporin. These aims will be accomplished using eight crystals of the recombinant unmyristylated catalytic subunit of protein kinase A and using the refined set of phases and methods of molecular replacement.